As a speech therapist, I don't recommend sippy cups since many of them promote a tongue thrust and improper oral positioning, which can negatively affect a child's speech and feeding development.  So ideally, particularly for those with developmental delays, it would be best to transition them straight to cup or straw drinking. 

However, I do understand their convenience, so if you are going to buy a sippy cup, it's important that it meets several guidelines: 

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•  Consider the size of the holes where the fluid comes out.  If the holes are too large, too much fluid will come out too quickly, which will make it difficult to manage swallowing.  If the holes are too small, it will be too difficult to draw liquid from the cup.

•  The best way to determine if the sippy cup is suitable is to try it out yourself, keeping in mind that your little one has a smaller mouth size.

•  What position is your tongue in?  Does your tongue go forward and under the spout?  The tongue should not protrude under the spout, but rest inside the mouth.

•  Is the spout too big, wide, long, and/or uncomfortable?  Is it difficult to close your lips around the spout?  Does the plastic taste funny?  If it is, imagine what it would be like for your child.

•  Is the spout too rigid?  It should be soft and flexible so that the tongue can position the spout instead of vice versa.

•  The next thing to do is to observe your child drinking from the cup.  The child should not be biting on the spout.  Check for teeth marks.  The lips should also be firmly closed around the spout so that no fluid leaks out of the corners of the mouth.

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The following video by Sandra Holtzmann is also helpful in understanding sippy cups and their effect on speech development:

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